Phase modulated power control

Abstract

An apparatus for applying AC power to a load while maintaining a minimum charge across a capacitor for use as a DC power supply, that may be connected in series with the power supply and load, and does not require a parallel connection to the power supply, including power control means responsive to the phase of the power supply signal such that the voltage across said power control means is allowed to rise to a given voltage each cycle, before power is applied to the load, and charging means operable to charge said capacitor to said given voltage.

I claim: 
     
       1. A method for applying AC power to a load while maintaining a voltage across a capacitor for use as a power supply without the need for a parallel connection to the AC power lines, comprising in combination the steps of: Applying power to the load through a switch, said switch being responsive to the AC power supply voltage such that it opens when the voltage passes through zero each cycle, and closes again when the voltage exceeds a preset threshold in either the positive or negative polarity;   charging a capacitor to the peak voltage present across said switch through a diode such that when the switch is always off and no power is applied to the load said capacitor is charged to a voltage equal to the peak power supply voltage, and when power is applied to the load the capacitor is charged to a voltage equal to either the positive or the negative switching threshold, determined by the polarity of said diode;   and feeding the voltage present across said capacitor through a voltage regulator to produce a constant voltage for use as a power supply.   
     
     
       2. A method as in claim 1 including the step of synchronizing the closing of said switch with an external clock signal such that the switch closes on the first clock transition that occurs after the power supply voltage has exceeded either the positive or negative threshold. 
     
     
       3. An apparatus for applying AC power to a load while maintaining a voltage across a capacitor for use as a DC power supply without the need for a parallel connection to the AC power lines, including: switching means connected in series with the AC power supply and load to apply power to the load, said switching means being responsive to the AC power supply voltage such that it opens when the voltage passes through zero twice each cycle, and closes again when the voltage exceeds a preset threshold in either the positive or negative polarity;   capacitor means and diode means connected across said switching means such that said capacitor is charged to the peak voltage present across the switching means;   and voltage regulator means connected to said capacitor means to produce a low regulated voltage suitable for powering external circuitry.   
     
     
       4. An apparatus as in claim 3 wherein said switching means is comprised of a TRIAC and switching control means, said TRIAC connected in series with the AC power supply and the load, and said control means being responsive to the voltage across the TRIAC such that it triggers the TRIAC when the voltage across the TRIAC exceeds a preset threshold in either the positive or negative polarity. 
     
     
       5. An apparatus as in claim 4 wherein said TRIAC control means is constructed using CMOS schmidt triggers and gates, with one side of the TRIAC used as circuit ground, and the inputs of two schmidt triggers connected to the other side of the TRIAC through high impedance resistive voltage dividers to allow sensing of the voltage across the TRIAC, the positive and negative switching thresholds being set by the values of the voltage dividers and the switching thresholds of the schmidt triggers, the gates being connected in a network such that the TRIAC is triggered whenever the voltage across the TRIAC exceeds either the positive or negative threshold. 
     
     
       6. An apparatus as in claim 3 wherein said switching means is comprised of a TRIAC and a synchronous switching control means, said TRIAC connected in series with the AC power supply and the load, and said synchronous control means being responsive both to the voltge across the TRIAC and an external clock such that it triggers the TRIAC on the first clock transition that occurs after the voltage across the TRIAC exceeds a preset threshold in either the positive or negative polarity. 
     
     
       7. An apparatus as in claim 6 wherein said synchronous switching control means is constructed using CMOS schmidt triggers, gates, and a D-type flip flop, with one side of the TRIAC used as circuit ground and the inputs of two schmidt triggers connected to the other side of the TRIAC through high impedance resistive voltage dividers to allow sensing of the voltage across the TRIAC, the positive and negative switching thresholds being set by the values of the voltage dividers and the switching thresholds of the schmidt triggers, the gates and flip flop being connected in a network such that the output of the flip flop goes high, triggering the TRIAC, on the first clock transition that occurs after the voltage across the TRIAC has exceeded either the negative or positive threshold. 
     
     
       8. An apparatus as in claim 3 wherein the voltage across said capacitor means is fed through a two stage zener diode voltage regulator to generate a constant low voltage, irrespective of whether the TRIAC is on or off.